Sen. Max Baucus, D-Mont. is seen on Capitol Hill in Washington. There is little mystery, from a campaign viewpoint, at least, about the eight senators who crossed party lines in Wednesday's showdown vote on background checks for gun buyers. The four Democrats who voted against broader background checks are from largely rural states that voted heavily against President Barack Obama last fall. (ASSOCIATED PRESS / J. Scott Applewhite, File)

WASHINGTON (AP) — There is little mystery, from a campaign viewpoint, at least, about the eight senators who crossed party lines in Wednesday’s showdown vote on background checks for gun buyers.

The four Democrats who voted against broader background checks are from largely rural states that voted heavily against President Barack Obama last fall.

Three of the four Republicans who voted in favor of the measure are from states Obama carried easily. The exception is John McCain of Arizona, the GOP’s 2008 presidential nominee.

The four Democrats — Max Baucus of Montana, Mark Begich of Alaska, Heidi Heitkamp of North Dakota and Mark Pryor of Arkansas — could cite a stack of pragmatic reasons for opposing the gun measure. The four Democrats’ states have deep traditions of hunting and gun ownership. They lack large cities, where persistent shootings can build momentum for gun control.

None of that saved the four Democrats from Obama’s wrath after the measure fell five votes short of the 60 needed to overcome a filibuster, a crushing defeat for Obama and others who want stronger measures to detect ineligible gun buyers.

In an emotional speech soon after the vote, the president — without naming names — said of the measure’s opponents: “Most of these senators could not offer any good reason why we wouldn’t want to make it harder for criminals and those with severe mental illnesses to buy a gun.”

“It came down to politics,” Obama said. “Obviously, a lot of Republicans had that fear, but Democrats had that fear, too. And so they caved to the pressure.”

Besides McCain, the four Republicans who voted for the bill are Sens. Susan Collins of Maine, Mark Kirk of Illinois, Obama’s home state, and Pat Toomey of Pennsylvania.

The four Democrats played down the unusual rebuke from their party’s president.

Baucus brushed off Obama’s comments, telling reporters, “He can say what he wants to say.” Baucus said he is comfortable with his vote, adding: “That’s my state.”

But Jon Tester, the other Democratic senator from Montana, where Obama lost by 13 percentage points last fall, drew a different conclusion and voted for the expanded background checks.

Lawmakers typically say they base their votes on principle, not pure politics. Yet one big difference between Tester and Baucus is hard to ignore: While Tester won’t face Montana voters again until 2018, Baucus is seeking a seventh term next year.

Likewise, Pryor is up for re-election next year in a state that Obama lost to Mitt Romney in a landslide, 61 percent to 37 percent. And Begich is seeking a second term next year in Alaska, a solidly Republican state that Obama lost by 14 points.

Heitkamp, just elected in a contest many expected her to lose, won’t run again until 2018. But her vote against the gun background-check proposal was in keeping with her widely praised campaign against Republican Rick Berg. Heitkamp inoculated herself on the gun issue by touting her “A” rating from the National Rifle Association.

When New York City Mayor Michael Bloomberg funded pro-gun control TV ads aimed at Heitkamp after the December elementary school massacre in Connecticut, the new senator wore them like an honor.

“I wouldn’t expect Mayor Bloomberg to follow my advice on how to run a major East Coast city,” she said, “and I don’t plan to follow his advice on what is best for North Dakotans.”

Some political strategists say elected Democrats in strongly pro-gun states face a no-win situation. That might apply to Pryor, a 10-year Senate veteran whose father, David, also was a senator from Arkansas.

The younger Pryor proved so popular that Republicans didn’t field a candidate against him in 2008. But Arkansas politics are shifting dramatically to the right.

Republican presidential nominees have carried the state by ever-larger margins over the past four elections. Two-term Democratic Sen. Blanche Lincoln was obliterated in 2010, losing her seat to Republican John Boozman by 21 percentage points.

Pryor waited until almost the last minute to announce his decision on the background-check measure. “It’s too broad, unworkable, and unreasonable for hunters and gun owners in our state,” he said.

A writer for the political website Arkansas Blog said, even before Pryor cast his vote, it’s “doubtful that he’ll get credit from the gun zealots for siding with them.”

The votes by Pryor, Baucus and Begich stand in contrast to those of two other Senate Democrats facing potentially tough races next year: Mary Landrieu of Louisiana and Kay Hagan of North Carolina. Both voted for the expanded background checks on gun buyers.

Hagan’s and Landrieu’s states have important characteristics lacking in their colleagues’ states, according to Ferrel Guillory, a Louisiana native and director of the Program on Public Life at the University of North Carolina at Chapel Hill.

Landrieu’s political base is in New Orleans, Guillory said, where her brother — like their father before them — is mayor, and where gun violence is a major problem. Landrieu may have little to gain by voting with the NRA.

“She’s not going to get the middle-income, middle-age male voter,” Guillory said, describing the typical Romney supporter. “She needs the newer electorate,” he said, which includes younger voters, minorities and high-tech workers in cities such as Baton Rouge.

North Carolina, which Republicans now control but which Obama carried in 2008, “is very narrowly divided,” Guillory said. Without Obama’s coattails next year, he said, Hagan “needs a strong turnout from blacks, Latinos, women.” They are unlikely to be moved by votes against incremental gun-control measures, he said.

Landrieu’s and Hagan’s decisions carry risks. They lack the political cover that would be provided if their state’s other senator were a Democrat also voting for the gun background proposal.

Like them, Begich, Pryor and Heitkamp share their states with Republican senators who voted against the Obama-backed measure.

On tough votes, Democratic lawmakers must weigh the risk of inviting a liberal challenger in the next primary versus the risk of antagonizing centrist voters in a general election.

Some liberal groups are calling for primary challenges to Baucus, Begich and Pryor. The California-based “Courage Campaign” is asking Democratic donors to withhold money from groups that back those three.

Local political activists doubt such tactics will work. In Montana, for instance, Baucus is a Democratic institution, and the state party leans heavily on his legacy and fundraising.

Alaska Democratic Party spokesman Zack Fields said there has been “zero discussion” of a primary challenge to Begich.

The electoral fates of Begich, Baucus, Pryor and Heitkamp will help determine whether Democrats can thrive in largely rural states.

The latest AP-GfK poll found significantly more support for gun rights in rural states. Among rural residents, 55 percent say someone in their household owns a gun, compared with 31 percent of suburban residents and 21 percent of urban dwellers.

Wednesday’s Senate vote reflected the rural nature of gun support.

The combined population of states in which both senators voted against the expanded gun background check — including Texas and Georgia — is about 78 million. The combined population of states on the losing side, in which both senators voted for the gun-control measure, was nearly double that number. That group included California, New York, Illinois, Pennsylvania, Michigan, New Jersey and Virginia.